Development of a circumstellar bubble during the main sequence in a high density, warm ISM (simulation F) with a 5 μG  interstellar magnetic field. From left to right this figure shows density and magnetic field lines at 1, 2, 4.3, and 4.5 Myr. The bubble is much smaller compared to the other 5 μG  simulations (B and E). The combined thermal and magnetic pressure in the ISM is strong enough to reduce the size of the bubble considerably. By the end of the main sequence (left side of right panel), the bubble has obtained a somewhat “eye-like” shape. At the onset of the red supergiant phase (right side of right panel), the hot, shocked wind bubble collapses under the combined forces of the interstellar magnetic field and the thermal pressure in the ISM.